Generally, drugs are given either orally or intravenously (IV). This is a systemic administration that distributes the drug all over the body, but requires a much larger dose. However, in local administration of drugs, the drug is delivered at the desired site, reducing the dose and the systemic side effects. With respect to cardiac problems, a drug can be mounted on a stent, balloon, a microcapsule, a special pellet, or any suitable local administration mechanism.
A stent is a medical device that is introduced to a body lumen. Typically, the stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e., by so-called “minimally invasive techniques.” The stent in a radially reduced configuration, optionally restrained in a radially compressed configuration by a sheath and/or catheter, is delivered by a stent delivery system, “introducer”, or a “catheter device” to the site where the stent is required. The introducer may enter the body from an access location outside of the body, such as through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means.
Stents and similar devices such as stent-grafts, expandable frameworks, and similar implantable medical devices, are radially expandable endoprostheses. These devices are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents can be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, fallopian tubes, coronary vessels, secondary vessels, etc. Stents may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or expanded by a combination of self-expansion and balloon expansion (hybrid expandable).
The stent can be created by methods including cutting or etching a design from a tubular stock, from a flat sheet that is cut or etched and is subsequently rolled, or from one or more interwoven wires or braids.
To prevent thrombosis and restenosis, and to treat vasculature tissue, there is a need to provide therapeutic agents directly at the site of stent deployment. One approach is through the use of a medicated stent to reduce the major proportion of the dosage amount of a drug administered via IV or orally. However, scientists have been working to develop a release profile of the medicated stent so that a minimal amount of a drug is given to the patient and, at the same time, having enhanced efficacy to cure thrombosis and restenosis.
In the field of angioplasty a guide catheter system for guiding an angioplasty balloon catheter into a patient's arterial system is known. Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for expanding a constricted area or stenosis in coronary arteries. It is also used for treatment of stenoses in other parts of the vascular system as well.
The most widely used form of angioplasty makes use of an angioplasty balloon catheter, which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the angioplasty balloon catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen connected to the balloon. The inflation of the balloon imparts a stretching force to the stenosis and artery wall to re-establish an acceptable blood flow through the artery. An angioplasty balloon catheter is normally introduced and directed through a patient's vascular system by a guide catheter. Guide catheters generally comprise a stiff shaft to provide support for the angioplasty balloon catheter as it is advanced through a patient's vascular system. The dimension of the guide catheter generally coincides with the insertion artery of a patient, and is generally large enough so that the angioplasty balloon catheter may easily insert therethrough to the coronary ostium. However, the dimension of the guide catheter is generally larger than the smaller dimension coronary arteries of the heart and thus its insertion through these arteries is restricted. In addition, the guide catheter is too stiff to negotiate the tortuous path of the coronary arteries. Thus, when a stenosis is located within these smaller dimension arteries, it is difficult for the guide catheter to provide assistance directly thereto. In this regard, discussed below are some of the conventional stent delivery systems, or “introducers” or “catheter devices”
Extra-Support Guide Wire/Guide Catheter or Both:
The shaft of guide wire is stronger than a standard wire and requires more force to buckle. However, this causes a concertina effect in vasculature (because of its strength or rigidity the vessel course changes) creating problems and also more likely to cause dissection.
While the use of the extra guide wires provides more support, using the extra guide wires results in a larger guide catheter. In this situation, guiding to the parent vessel makes the procedure difficult, time consuming and may also cause extra blood loss. Puncture site problems are also increased due to the larger diameter guide catheter causing an increase in hematoma or pseudo-aneurysm. Also, stent deployment becomes more difficult as the extra guide wires have to be withdrawn.
Over the Wire Balloon:
Using an over the wire balloon after the guide-wire has already crossed the lesion means using a doc/link or other guide wire lengthening device to switch to the over the wire balloon. However, such a technique creates difficulties of not using a rapid exchange balloon catheter.
Deep Throat Guide:
In this technique, a guiding catheter is pushed inside the artery. This offers more length before the guide catheter is pushed far back in the aortic root. However, the deep throat guide is associated with dissection in the artery with issues of the left main, proximal left anterior descending (LAD) or left circumflex (LCx) or ostial/proximal right coronary artery (RCA) dissection and complications as described above. It is also associated with severe spasms of the proximal part of the artery.
Anchoring Balloon:
In this technique, in another small artery, a separate wire and small balloon are inflated to act as an anchor. However, changing to a larger guide predisposes the patient to problems as described above in the extra guide wire section. This technique also causes restenosis in the anchored balloon segment of the artery and can also cause tearing or avulsion of this segment with disastrous consequences.
Undertreat:
Sometimes in above situation a smaller diameter balloon is dilated initially. However, stent deployment is not possible at a later time and the lesion is therefore undertreated.
Rotablator:
The steps to change to a large size guide catheter lead to the associated problems described above, and the chance of restenosis is increased greatly.
Certain guide catheters provide extra-support (e.g., amplatzer, etc.), because the curvature of the catheters is designed to make use of the opposite aortic wall. Thus, the catheters will require more force than standard guide catheters to be pushed back. However, these types of catheters are more difficult to maneuver in the aortic root and are more likely to injure proximal vessels (e.g., the left main or proximal RCA). This has serious consequences to the left main/proximal RCA dissection. For instance, it may result with stenting an unprotected left main and causing lifetime dual antiplatelet therapy, which have serious long-term consequences.
In addition, the main problems after percutaneous transluminal coronary angioplasty (PTCA) and stent implantation are:
Restenosis:
The occurrence of restenosis causes loss of lumen and, thus, blocks the artery again. Restenosis is caused by smooth muscle cell hyperplasia and intracellular matrix.
Stent Thrombosis:
This occurs due to the clot formation over the stent. This is rare as compared to restenosis but has sudden onset and presents an acute myocardial infarction (i.e., heart attack) and has devastating consequences. The clot has two principal components, fibrin meshwork and platelets.
Scientists and medical practitioners have observed that while the standard balloon catheter along with stent is placed in the coronary or peripheral artery by a conventional catheter delivery system, the following limitations can be encountered:    a) In case that there is an obstruction in the coronary or peripheral artery in its path, such obstruction restricts the movement of the catheter. In such situations, if the catheter is further pushed, the guide wire-balloon assembly will start curving down and finally the guide wire with the balloon will fall back as shown in FIGS. 1B and 1C.    b) In some situations, when the angioplasty is carried out, and balloon is being pulled back, firstly it is pushed and then pulled back sequentially. However, sometimes during pulling back, the balloon tends to get stuck and thus in the assembly the length of the balloon catheter is being reduced, to accommodate the reduced length of the balloon catheter, the guide catheter will be sucked inside the artery as shown in the FIGS. 1(D-E). This sucking of guide catheter can dissect distal left main and proximal LAD, which can in turn cause serious repercussions to the patient.    c) Often it is noticed that the stent comes out of the balloon and embolisms occur somewhere in the vascular bed.